To reduce discharge of fuel vapors into the atmosphere, motor vehicles induct fuel vapors from a fuel tank into the engine. An evaporative emission control system including a carbon canister is also coupled to the fuel tank to adsorb fuel vapors under some conditions when the internal combustion engine is not running. The carbon canister, however, has limited capacity, thus engine running manifold vacuum may be used to desorb the vapor from the carbon canister via opening of a purge valve. Desorbed vapors are combusted in engine.
Diagnostics may be performed on the evaporative emission control system, e.g., to detect leaks in the system. For example, diagnostics may be performed to test for leaks in the emission control system during engine off conditions, e.g., after a vehicle key off, to mitigate noise factors associated with vehicle dynamics such as road feedback, sharp-turn G forces, fuel sloshing, etc. During leak detection execution, a controller may operate in a low power mode with some sensors in the system depowered, e.g., a fuel level sensor may be turned off during leak detection.
The inventors herein recognize that a refueling event is a major noise factor that can skew leak detection results as it introduces vapors into the tank. For example, with natural vacuum leak detection, a refueling event can result in a false pass if not detected properly. As another example, with vacuum-pump based leak detection, a refueling event can result in a false fail if not detected. Thus, it is desirable for a controller to detect a refueling event and abort any leak detection algorithm execution in response to detection of the refueling event. In some approaches, a fuel tank pressure sensor may be used to infer a refueling event. However, such approaches are prone to false refueling determinations during certain conditions, e.g., if the vehicle is being towed, a trunk is opened and slammed shut, someone sits on the car and shakes it, etc.
In one example approach to at least partially address these issues, a method for a vehicle with an engine comprises discontinuing leak diagnostics in response to a temperature change in a fuel vapor canister coupled to a fuel tank in an emission control system while the leak diagnostics are being performed in the emission control system. For example, during refueling, vapors dispensed by a refueling pump may be adsorbed in the canister leading to a temperature rise in the canister. This change in temperature may be used as an indication that refueling is occurring or has occurred for the particular engine off condition during which the diagnostics are being performed by a controller in the vehicle. Such identification may occur in the absence of a fuel tank pressure sensor, independent of a fuel tank pressure sensor, or in response to degradation of a fuel tank pressure sensor. In another aspect, the identification may also occur in response to both a pressure sensor and detection of a predetermined temperature change in the canister.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.